1. Field of the Invention
The present invention relates to a method of controlling a photographic emulsion manufacturing process. More particularly, the invention pertains to a control method by non-linear approximation for a photographic emulsion manufacturing process which involves a multiplicity of variables.
2. Description of the Prior Art
Photographic emulsion which are employed for photosensitive materials, such as photographic paper and film, generally include silver halide as a principal component. Silver halide is a compound of a halogen, such as Br, and silver, and is widely used as a material for photographic emulsions. Such silver halide is produced by crystallization in which silver nitrate (AgNO.sub.3) and potassium bromide (KBr) or potassium iodide (KI) or sodium chloride (NaCl) are added together such that they react to crystallize silver halide.
In this type of reaction crystallization step, it is not possible to directly measure the degree of crystal growth of silver halide itself. For this reason, it is conventional practice to estimate the degree of growth of silver halide from the silver concentration in the solution which is related to the growth of silver halide.
In the process of crystal growth of silver halide, a considerable number of operations in the control of crystal growth are conducted based on the operator's experience, since some of the mechanism of the crystal growth has not yet been satisfactorily elucidated. Further, in the crystal growth process of the above-described type, the growth of crystals of silver halide is affected by various factors, such as the solution temperature and the rate of stirring, in addition to the silver concentration and the halogen concentration in the solution. A change in even one of these process variates has an effect on the other variates. In such a control (multivariable control) in which a change in one of the process variates affects the other variates, it is not possible according to the conventional PID control to effect control in such a manner that process variates as objects of measurement are measured, and the respective manipulated variables of the measured variates are simultaneously and automatically controlled so that each controlled variable coincides with a desired value.